Some restructuring in test suite
Added sample testing.grass file containing Grass source code (it can be compiled with grassc)
Added new modifier, refactored declaratio tranlsation into its own method
Refactored definitnion translation into its own method
Added tests for and implemented working `infer` modifier in instant
definitions
Tested supplying values in instant definitions via references
Suplying value in instant definition via reference fails when referenced
field has no defined value
Definitions and redefinitions are handled by the same method